arXiv subjects

Jacob Rubinstein

Publications and source records attributed to Jacob Rubinstein.

10 recordsLinked to original sources

arXiv2026

Weighted least action principle for Maxwell equations

The Fermat principle of least time determines the path of a single ray of light given its initial and final positions and the medium electromagnetic properties. However, a single ray is not a measurable physical object. We derive here an upgraded variational principle for the geometric optics limit of Maxwell equations in an arbitrary medium, based on measuring the intensity of the wave on two planes. The principle provides the complete Fresnel rays bundle connecting associated points at the first and second planes. One of the applications of the present theory is to use the reciprocity between Fresnel rays and phase normals to determine the phase of an electromagnetic wave from two intensity measurements.

math-ph↗

arXiv2026

Advancing Digital Twin Generation Through a Novel Simulation Framework and Quantitative Benchmarking

The generation of 3D models from real-world objects has often been accomplished through photogrammetry, i.e., by taking 2D photos from a variety of perspectives and then triangulating matched point-based features to create a textured mesh. Many design choices exist within this framework for the generation of digital twins, and differences between such approaches are largely judged qualitatively. Here, we present and test a novel pipeline for generating synthetic images from high-quality 3D models and programmatically generated camera poses. This enables a wide variety of repeatable, quantifiable experiments which can compare ground-truth knowledge of virtual camera parameters and of virtual objects against the reconstructed estimations of those perspectives and subjects.

cs.CV↗

arXiv2025

A mathematical model for the progression of dental caries

A model for the progression of dental caries is derived. The analysis starts at the microscopic reaction and diffusion process. The local equations are averaged to derive a set of macroscopic equations. The global system includes features such as anisotropic diffusion and local changes in the geometry due to the enamel melting. The equations are then solved numerically. The simulations highlight the effect of anisotropy. In addition we draw conclusions on the progression rate of caries, and discuss them in light of a number of experiments.

physics.med-ph↗

arXiv2021

A flexible anatomical set of mechanical models for the organ of Corti

We built a flexible platform to study the mechanical operation of the organ of Corti (OoC) in the transduction of basilar membrane (BM) vibrations to oscillations of an inner hair cell bundle (IHB). The anatomical components that we consider are the outer hair cells (OHCs), the outer hair cell bundles, Deiters cells, Hensen cells, the IHB and various sections of the reticular lamina. In each of the components we apply Newton's equations of motion. The components are coupled to each other and are further coupled to the endolymph fluid motion in the subtectorial gap. This allows us to obtain the forces acting on the IHB, and thus study its motion as a function of the parameters of the different components. Some of the components include a nonlinear mechanical response. We found that slight bending of the apical ends of the OHCs can have a significant impact on the passage of motion from the BM to the IHB, including critical oscillator behaviour. In particular, our model implies that the components of the OoC could cooperate to enhance frequency selectivity, amplitude compression and signal to noise ratio in the passage from the BM to the IHB. Since the model is modular, it is easy to modify the assumptions and parameters for each component.

physics.bio-ph↗

arXiv2020

Reduced equations for an active model of the hydroelastic waves in the cochlea

Building upon our earlier passive models for the cochlea, here we enhance the model with an active mechanism. Starting with a one-chamber simplification leading to a system of a time-dependent PDE in two spatial variables for the pressure coupled to a PDE in one spatial variable for the oscillation of the basilar membrane, we rigorously establish the validity of a dimension reduction to a system to two ODE's. We then present numerical simulations demonstrating the ability of this reduced active system to distinguish and amplify multi-frequency input signals.

math.AP↗

arXiv2013

Kinematic and dynamic vortices in a thin film driven by an applied current and magnetic field

Using a Ginzburg-Landau model, we study the vortex behavior of a rectangular thin film superconductor subjected to an applied current fed into a portion of the sides and an applied magnetic field directed orthogonal to the film. Through a center manifold reduction we develop a rigorous bifurcation theory for the appearance of periodic solutions in certain parameter regimes near the normal state. The leading order dynamics yield in particular a motion law for kinematic vortices moving up and down the center line of the sample. We also present computations that reveal the co-existence and periodic evolution of kinematic and magnetic vortices.

math.AP↗

arXiv2007

The resistive state in a superconducting wire: Bifurcation from the normal state

We study formally and rigorously the bifurcation to steady and time-periodic states in a model for a thin superconducting wire in the presence of an imposed current. Exploiting the PT-symmetry of the equations at both the linearized and nonlinear levels, and taking advantage of the collision of real eigenvalues leading to complex spectrum, we obtain explicit asymptotic formulas for the stationary solutions, for the amplitude and period of the bifurcating periodic solutions and for the location of their zeros or "phase slip centers" as they are known in the physics literature. In so doing, we construct a center manifold for the flow and give a complete description of the associated finite-dimensional dynamics.

math-ph↗

arXiv1998

Flux-Induced Vortex in Mesoscopic Superconducting Loops

We predict the existence of a quantum vortex for an unusual situation. We study the order parameter in doubly connected superconducting samples embedded in a uniform magnetic field. For samples with perfect cylindrical symmetry, the order parameter has been known for long and no vortices are present in the linear regime. However, if the sample is not symmetric, there exist ranges of the field for which the order parameter vanishes along a line, parallel to the field. In many respects, the behavior of this line is qualitatively different from that of the vortices encountered in type II superconductivity. For samples with mirror symmetry, this flux-induced vortex appears at the thin side for small fluxes and at the opposite side for large fluxes. We propose direct and indirect experimental methods which could test our predictions.

cond-mat.supr-con↗

arXiv1996

Design for the Detection of the Singly-Connected Superconducting State

We study the Little-Parks effect for mesoscopic loops with very nonuniform thickness. The results follow the trend of the phase diagram obtained for almost uniform thickness. In particular, the singly-connected state is stable on a line segment delimited by two critical points. Most of this study considers loops with piecewise constant thickness; in this case the Euler-Lagrange equation can be integrated analytically. Under appropriate conditions, the temperature range where the singly-connected state is stable is proportional to the square of the ratio between the maximal and the minimal thicknesses. Our results may serve as a guide for planning experiments.

cond-mat.supr-con↗

arXiv1996

Topology and Phase Transitions in the Little-Parks Experiment

This is an analytic study of the problem of transitions between normal and superconducting phases for a sample which encloses a magnetic flux. A preliminary study of this problem, based on numerical minimization of the free energy for a particular form of the thickness of the sample, was published in Phys. Rev. Lett. {\bf 75}, 320 (1995). For a sample of uniform thickness the order parameter is uniform, but even infinitesimal deviations from uniform thickness give rise to a singly connected state in which the order parameter vanishes at a suitable layer, so that the superconducting part does not enclose the magnetic field. The stability domain of this singly connected state is a line segment in the magnetic field-temperature plane, delimited by two critical points. The phase diagram contains several bifurcation lines, which are systematically analyzed.

supr-con↗